The invention concerns the genomic and cDNA sequences of the PCTA-1 gene, biallelic markers of the PCTA-1 gene and the association established between these markers and prostate cancer. The invention provides means to determine the predisposition of individuals to prostate cancer as well as means for the diagnosis of this cancer and for the prognosis/detection of an eventual treatment response to therapeutic agents acting against prostate cancer.
The incidence of prostate cancer has dramatically increased over the last decades. It averages 30-50/100,000 males in Western European countries as well as within the US White male population. In these countries, it has recently become the most commonly diagnosed malignancy, being one of every four cancers diagnosed in American males. Prostate cancer""s incidence is very much population specific, since it varies from 2/100,000 in China, to over 80/100,000 among African-American males.
In France, the incidence of prostate cancer is 35/100,000 males and it is increasing by 10/100,000 per decade. Mortality due to prostate cancer is also growing accordingly. It is the second cause of cancer death among French males, and the first one among French males aged over 70. This makes prostate cancer a serious burden in terms of public health.
Prostate cancer is a latent disease. Many men carry prostate cancer cells without overt signs of disease. Autopsies of individuals dying of other causes show prostate cancer cells in 30% of men at age 50 and in 60% of men at age 80. Furthermore, prostate cancer can take up to 10 years to kill a patient after the initial diagnosis.
The progression of the disease usually goes from a well-defined mass within the prostate to a breakdown and invasion of the lateral margins of the prostate, followed by metastasis to regional lymph nodes, and metastasis to the bone marrow. Cancer metastasis to bone is common and often associated with uncontrollable pain.
Unfortunately, in 80% of cases, diagnosis of prostate cancer is established when the disease has already metastasized to the bones. Of special interest is the observation that prostate cancers frequently grow more rapidly in sites of metastasis than within the prostate itself.
Early-stage diagnosis of prostate cancer mainly relies today on Prostate Specific Antigen (PSA) dosage, and allows the detection of prostate cancer seven years before clinical symptoms become apparent. The effectiveness of PSA dosage diagnosis is however limited, due to its inability to discriminate between malignant and non-malignant affections of the organ and because not all prostate cancers give rise to an elevated serum PSA concentration. Furthermore, PSA dosage and other currently available approaches such as physical examination, tissue biopsy and bone scans are of limited value in predicting disease progression.
Therefore, there is a strong need for a reliable diagnostic procedure which would enable a more systematic early-stage prostate cancer prognosis.
Although an early-stage prostate cancer prognosis is important, the possibility of measuring the period of time during which treatment can be deferred is also interesting as currently available medicaments are expensive and generate important adverse effects. However, the aggressiveness of prostate tumors varies widely. Some tumors are relatively aggressive, doubling every six months whereas others are slow-growing, doubling once every five years. In fact, the majority of prostate cancers grow relatively slowly and never becomes clinically manifest. Very often, affected patients are among the elderly and die from another disease before prostate cancer actually develops. Thus, a significant question in treating prostate carcinoma is how to discriminate between tumors that will progress and those that will not progress during the expected lifetime of the patient.
Hence, there is also a strong need for detection means which may be used to evaluate the aggressiveness or the development potential of prostate cancer tumors once diagnosed.
Furthermore, at the present time, there is no means to predict prostate cancer susceptibility. It would also be very beneficial to detect individual susceptibility to prostate cancer. This could allow preventive treatment and a careful follow up of the development of the tumor.
A further consequence of the slow growth rate of prostate cancer is that few cancer cells are actively dividing at any one time, rendering prostate cancer generally resistant to radiation and chemotherapy. Surgery is the mainstay of treatment but it is largely ineffective and removes the ejaculatory ducts, resulting in impotence. Oral oestrogens and luteinizing releasing hormone analogs are also used for treatment of prostate cancer. These hormonal treatments provide marked improvement for many patients, but they only provide temporary relief. Indeed, most of these cancers soon relapse with the development of hormone-resistant tumor cells and the oestrogen treatment can lead to serious cardiovascular complications. Consequently, there is a strong need for preventive and curative treatment of prostate cancer.
Efficacy/tolerance prognosis could be precious in prostate cancer therapy. Indeed, hormonal therapy, the main treatment currently available, presents important side effects. The use of chemotherapy is limited because of the small number of patients with chemosensitive tumors. Furthermore the age profile of the prostate cancer patient and intolerance to chemotherapy make the systematic use of this treatment very difficult.
Therefore, a valuable assessment of the eventual efficacy of a medicament to be administered to a prostate cancer patient as well as the patient""s eventual tolerance to it may allow the benefit/risk ratio of prostate cancer treatment to be enhanced.
WO 96/21671 describes a new protein, named PCTA-1. The document describes the cloning and sequencing of a cDNA encoding PCTA-1 (GenBank L78132). This cDNA has 3.85 kb in length and presents about 80% sequence homology with rat galectin-8.
WO 96/21671 mentions that the PCTA-1 protein retains a number of conserved structural motifs that are found in most members of the galectin gene family. On the basis of its predicted amino acid sequence, PCTA-1 is said to appear to be a human homologue of rat galectin-8. The galectins display wide tissue distribution, clear developmental regulation, and differential levels in specific tissues, supporting the hypothesis that they contribute to many physiologically important processes in mammalian cells. Of direct relevance to cancer is the finding that the galectins can mediate both cell-cell and cell-matrix interactions.
The inventors have characterized the genomic sequence of the PCTA-1 gene, including its regulatory regions, and, through an association study, have shown that alleles of some biallelic markers of PCTA-1 are associated with prostate cancer.
Therefore, the present invention concerns the identification and characterization of the genomic sequence of the PCTA-1 gene, of new cDNA sequences and the proteins encoded by these cDNAs. The invention also concerns biallelic markers located in such sequences, as well as the selection of significant polymorphisms associated with prostate cancer.
Oligonucleotide probes and primers hybridizing specifically with a genomic sequence of PCTA-1 are also part of the invention. A further object of the invention consists of recombinant vectors comprising any of the nucleic acid sequences described in the present invention, and in particular of recombinant vectors comprising the regulatory region of PCTA-1 or a sequence encoding a PCTA-1 protein, as well as cell hosts comprising said nucleic acid sequences or recombinant vectors.
The selected polymorphisms are used in the design of assays for the reliable detection of genetic susceptibility to prostate cancer, of an early onset of prostate cancer, of the aggressiveness of prostate cancer tumors, of a modified or forthcoming expression of the PCTA-1 gene, of a modified or forthcoming production of the PCTA-1 protein, or of the production of a modified PCTA-1 protein. They can be used for diagnosis, staging, prognosis, and monitoring of such a disease, which processes can be further included within treatment approaches. The selected polymorphisms can also be used in the design of drug screening protocols to provide an accurate and efficient evaluation of the therapeutic and side-effect potential of new or already existing medicaments.
The invention also encompasses methods of screening of molecules which modulate or inhibit the expression of the PCTA-1 gene and more preferably of agent acting against prostate cancer.